An urgent problem still facing the United States is that of creating and maintaining ship channels through pack ice sufficient for economical shipboard transport of oil. On the Great Lakes there is need for all-year transport by ship, but now available. Experience with very large icebreakers such as the Manhattan defines the problem as: (1) not so much that of breaking the ice but instead of removing the ice broken so that the broken ice does not wedge the sides of the ship between unbroken ice bounding the channel and so that the icebreaker smash is cleanly against yet-to-be broken ice rather than against an energy absorbing cushion of floating ice blocks caught in the channel between ship and ice pack, and (2) that of leaving an unobstructed or broken and slow-to-freeze channel to the rear for other ships to follow.